The national capital was enveloped in a thick blanket of fog on Saturday morning as the minimum temperature settled at 8.4 degrees Celsius.
Visibility was reduced to 50 metres in Palam at 5.30 am, a MeT Department official said.
Around 20 north-bound trains were delayed by two to five hours due to the fog, a Northern Railways spokesperson said.
Relative humidity was 100 per cent at 8.30 am.
The fog is expected to disperse later in the day and the maximum temperature is likely to hover around 18 degrees Celsius, said the official.
By 9 am, the air quality index of Delhi was recorded at 240 which was in the 'poor' category, as per data of Central Pollution Control Board.
On Friday, the minimum temperature was 11.3 degrees Celsius and the maximum 17.7 degrees Celsius.